As to a vehicle provided with an engine capable of controlling an engine output torque independently of a driver's accelerator pedal manipulation, and an automatic transmission, there is a concept of “driving force control”, in which positive or negative target driving torque calculated based on a driver's accelerator pedal manipulated amount, vehicle driving conditions and the like is realized by the engine torque and a transmission gear ratio of the automatic transmission. Similar control schemes are those referred to as “a driving force request type”, “a driving force demand type”, and “a torque demand scheme”.
An engine control apparatus of the torque demand scheme calculates a target torque of the engine based on an accelerator manipulation amount, an engine speed and an external load, and controls a fuel injection amount and an air supply amount.
In such an engine control apparatus of the torque demand scheme, practically, a loss load torque such as frictional torque that would be lost in the engine or the powertrain system is considered additionally to a requested output torque, to calculate a target generated torque. The fuel injection amount and the air supply amount are controlled to realize the calculated target generated torque.
According to the engine control apparatus of the torque demand scheme, the engine torque, which is the physical quantity directly effecting the control of the vehicle, is employed as the reference value of control. This improves the drivability, e.g., constant steering feeling is always maintained.
Japanese Patent Laying-Open No. 2005-178626 discloses a vehicle integrated control system that improves the fail-safe performance in such an engine control apparatus of the torque demand type. The vehicle integrated control system includes a plurality of control units controlling a running state of a vehicle based on a manipulation request, and a processing unit generating information to be used at respective control units in prohibiting an operation of a vehicle, based on information on a position of the vehicle and providing the generated information to each control unit. Each control unit includes sensing means for sensing an operation request with respect to at least one control unit, and calculation means for calculating information related to a control target to manipulate an actuator set in correspondence with each unit using at least one of the information generated at the processing unit and the sensed operation request.
According to the vehicle integrated control system, the plurality of control units include, for example, one of a driving system control unit, a brake system control unit, and a steering system control unit. The driving system control unit senses an accelerator pedal manipulation that is a request of a driver through the sensing means to generate a control target of the driving system corresponding to the accelerator pedal manipulation using a driving basic driver model, whereby a power train that is an actuator is controlled by control means. The brake system control unit senses a brake pedal manipulation that is a request of the driver through the sensing means to generate a control target of the brake system corresponding to the brake pedal manipulation using a brake basic driver model, whereby a brake device that is an actuator is controlled by the control means. The steering system control unit senses a steering manipulation that is a request of the driver through the sensing unit to generate a control target of the steering system corresponding to the steering manipulation using a steering basic driver model, whereby a steering device that is an actuator is controlled by the control means. The vehicle integrated control system includes a processing unit that operates parallel to the driving system control unit, the brake system control unit and the steering system control unit that operate autonomously. For example, the processing unit generates: 1) information to be used at respective control means based on environmental information around the vehicle or information related to the driver, and provides the generated information to respective control units; 2) information to be used at respective control means to cause the vehicle to realize a predetermined behavior, and provides the generated information to respective control units; and 3) information to be used at respective control means based on the current dynamic state of the vehicle, and provides the generated information to respective control units. Each control unit determines as to whether or not such input information, in addition to the driver's request from the processing unit, is to be reflected in the motion control of the vehicle, and to what extent, if to be reflected. Each control unit also corrects the control target, and transmits the information among respective control units. Since each control unit operates autonomously, the power train, brake device and steering device are controlled eventually at respective control units based on the eventual driving target, braking target and steering target calculated from the driver's manipulation information sensed by the sensing unit, the information input from the processing unit, and information transmitted among respective control units. Thus, the driving system control unit corresponding to a “running” operation that is the basic operation of the vehicle, the brake system control unit corresponding to a “stop” operation, and the steering system control unit corresponding to a “turning” operation are provided operable in a manner independent of each other. The processing unit is applied with respect to these control units such that the driving operation corresponding to the vehicle environment, driving support for the driver, and vehicle dynamic motion control can be conducted automatically in a parallel manner. Accordingly, decentralized control is allowed without a master control unit that is positioned at a higher level than the other control units, and the fail safe faculty can be improved. Furthermore, by virtue of autonomous operation, development is allowed on the basis of each control unit or each processing unit. In the case where a new driving support function is to be added, the new function can be implemented by just adding a processing unit or modifying an existing processing unit. As a result, a vehicle integrated control system can be provided, having the fail-safe performance improved and capable of readily accommodating addition of a vehicle control function, based on integrated control, without realizing the entire control of the vehicle by, for example, one master ECU (Electronic Control Unit) as in the conventional case. In addition, as this processing unit, a unit generating information to be used in each control unit in prohibiting a sudden operation of a vehicle and providing the generated information to each control unit is arranged. For example, when the vehicle is parked in a vacant parking space in a parking lot, information that sudden acceleration/deceleration risk is “high” is generated and provided to each control unit. Upon receiving such information, each control unit controls the driving system control unit, the brake system control unit and the steering system control unit so as to prohibit a sudden operation. In this manner, the vehicle integrated control system capable of avoiding inadvertent sudden acceleration/deceleration can be provided.
In the integrated control system disclosed in the above-described Japanese Patent Laying-Open No. 2005-178626, a requested driving force (target driving force) of a manipulating system calculated from the position of the accelerator pedal manipulated by the driver and a requested driving force (target driving force) of a driving support system such as cruise control are arbitrated between each other, to generate an instruction value for controlling an actuator controlling the engine that is the driving power source or an actuator controlling the transmission ratio of the transmission.
Arbitration between such target values (requested values) from respective system must be carried out with a physical quantities of one unified unit (dimension) such as acceleration, driving force, torque and the like. This arbitration may result in an arithmetic error or the reduced number of significant figures because of the conversion and the reverse conversion, when the value must be returned to the original unit. Thus, a difference from the originally requested quantity may be generated. More specifically, when a requested torque of the manipulating system, i.e., an original target engine torque, must be arbitrated between a target driving force of the supporting system, the original target engine torque of the manipulating system must be converted into the target driving force of the manipulating system. The converted target driving force of the manipulating system and the target driving force of the supporting system without needing conversion are arbitrated between each other. If the target driving force of the manipulating system is selected as a result, the converted target driving force of the manipulating system is reversely converted to calculate the target engine torque of the manipulating system. Using the target engine torque of the manipulating system calculated by such reverse conversion, an actuator controlling the engine (such as the motor for driving the throttle valve) is controlled. Here, what becomes a concern is the poor accuracy of the target engine torque of the manipulating system obtained through reverse conversion and actually used in controlling the engine relative to the original target engine torque of the manipulating system. There is a problem that conversion into the unit of driving force and the reverse conversion into the unit of torque may invite an arithmetic error or the reduced number of significant figures, resulting in an error contained in the originally requested engine torque.
However, the vehicle integrated control system disclosed in Japanese Patent Laying-Open No. 2005-178626 is silent about such a problem.